The present invention relates generally to lifting tools. More particularly, the present invention relates to lifting tools for automatic centering and 180 degree rotation of large objects, such as rectangular transformer tanks
It is often necessary to lift large, heavy objects during a manufacturing process, such as, for example, during the process of painting steel enclosures (known as xe2x80x9ctanksxe2x80x9d) for pad mounted transformers. Transformer tanks are usually either cylindrical or rectangular, and are typically painted in an automatic paint facility.
Before the tanks are painted, however, they are typically processed through a manual xe2x80x9cshot blastxe2x80x9d machine that uses small steel grit to prepare the tank surface for painting. Cylindrical tanks typically arrive at the shot blast machine open end up. To ensure that the steel grit does not accumulate inside the tank, each tank must be turned upside down and centered on a table that carries the tank into the shot blast machine. The table rotates during the blasting operation so that the perimeter of the tank can be properly blasted. Cylindrical tanks typically have attachments, known as xe2x80x9clifting tugs,xe2x80x9d that provide a place to hook the tank using a hoist, and allow it to lean over several degrees and be placed on its side on the table. Then, a bottom loop on the tank is hooked to pull the tank up vertically, and set it down on its open end. Cylindrical tanks remain upside down for subsequent operations in the painting process.
This method of tank rotation has proven to be ineffective for rectangular tanks, however. Due to the placement of attachments, the tank is more difficult to control safely as it is picked up, and is awkward to handle as it is placed on the table on its side and then turned upside down and centered. This is especially true for rectangular tanks, as it is desirable to turn the tanks over again, after the manual shot blast operation, to keep them open end up for the subsequent operations in the painting process. Again, it is awkward and takes effort to pick up the tanks from the table and place them on a transport cart easily and safely.
As a tank typically weighs more than 50 pounds (and frequently up to as much as 100 pounds or more), a tank is too heavy and too large for an ordinary person to manipulate without the aid of a lifting tool. Copending application Ser. No. 09/473,887, entitled xe2x80x9cLifting Tool For Safe 90 Degree Rotation,xe2x80x9d discloses and claims a lifting tool for safe 90 degree rotation of large heavy objects. Copending application Ser. No. 09/473,880, entitled xe2x80x9cLifting Tool For Safe 105 Degree Rotation,xe2x80x9d discloses and claims a lifting tool for safe 105 degree rotation of large heavy objects. The lifting tools described in these applications, while suitable for 90 and 105 degree rotation, respectively, are not optimal for rotation of up to 180 degrees. Thus, there is a need in the art for a lifting tool that can be used for automatic centering and 180 degree rotation of large objects, such as rectangular transformer tanks.
The present invention satisfies these needs in the art by providing lifting tools for automatic centering and 180 degree rotation of large objects, such as rectangular transformer tanks. A lifting tool according to the present invention includes a first rail, which is adapted to be coupled to a first end of the object, and a second rail, which adapted to be coupled to a second end of the object. Two sets of inversion linkage are coupled to ends of the rails.
Each set of inversion linkage includes a pivot pin and a plurality of components that cooperate to move the pivot pin to coincide with the center of gravity of an object that the tool has been sized and shaped to lift and invert. Specifically, inversion linkage for lifting and inverting rectangular enclosures, such as transformer tanks, can include a first telescoping member, and a second telescoping member slidably coupled to the first telescoping member. The second telescoping member moves axially relative to the first telescoping member. The slider rail is fixedly connected to an exterior of the first telescoping member, and has a slot elongated along a length thereof.
The linkage also includes a first rotational member, which is fixedly coupled to the first telescoping member, and a second rotational member, which is rotationally coupled to the first rotational member. The second rotational member has a slot elongated along a length thereof, and is coupled to the slider rail by the pivot pin, which extends through both the slider rail slot and the second rotational member slot. When the second telescoping member is moved axially relative to the first telescoping member, the pivot pin also moves axially relative to the first telescoping member. The distance by which the pivot pin moves is proportional to the distance by which the second telescoping member is moved. Thus, when the tool is sized to fit a particular enclosure (by moving the second telescoping member relative to the first), the pivot pin automatically moves in coincidence with the center of gravity of the enclosure.
The lifting tool can also include a third rotational member, which is rotationally coupled to the second rotational member, and a fourth rotational member, which is rotationally coupled to the third rotational member and fixedly coupled to the second telescoping member.
The lifting tool can also include an enclosure grasping assembly coupled to the second rail, which is adapted to couple the second rail to the second end of the object. The enclosure grasping assembly can include a first structural angle, which is fixedly coupled to the second rail, and a second structural angle, which is fixedly coupled to the first structural angle so as to form a groove between the structural angles for receiving the second end of the object.